1. Field of the Invention
This invention relates to a method for estimating a reverberation signal component of an acoustic signal, a method for dereverberation of the acoustic signal and to a system therefore. The invention relates particularly to the dereverberation of a microphone signal in a room or a vehicle cabin.
2. Related Art
The enhancement of the quality of audio and speech signals in a communication system is a central topic in acoustic, and in particular, speech signal processing. The communication between two parties is often carried out in a noisy background environment and noise reduction, as well as echo compensation, is necessary to guarantee intelligibility. Prominent examples are hands-free voice communication systems in vehicles and automatic speech recognition units.
Of particular importance is the suppression of reverberation that can severely affect the quality of the audio signal. Reverberation especially impairs the performance of automatic speech recognizers. The acoustic phenomenon of reverberation can be described as follows: a sound source (e.g., a speaking person or a loudspeaker) emanates an acoustic signal that propagates through the room. After the sound reaches the microphone in a direct path, further sound from the reflection of the sound off room boundaries also reach the microphone, but with some delay. Depending on the strength of the reflections and their time delays, the speech spectrum smears over time.
Several methods for the dereverberation of microphone signals are known in the art. For example, it is attempted to reduce dereverberation by means of deconvolution, i.e., inverse filtering using an estimate for the acoustic channel. Deconvolution can be performed in the time domain or in the cepstral domain. This kind of signal processing, however, suffers from the dependence on accurate estimate of the acoustic channel which is in practical applications almost impossible. In an alternative approach, the direct path speech signal is processed by pitch enhancement or by linear predictive coding analysis. In a multi channel approach, averaging over multiple microphone signals is performed to obtain a reduction of the reverberation contribution to the processed signal. These approaches cannot, however, guarantee a sufficiently high quality of the wanted signal. In addition, implementations of the multi channel approaches are rather expensive.
Despite recent engineering processes, current dereverberation techniques are still not satisfying and reliably enough for practical applications. Accordingly, a need exists to overcome the above-mentioned drawbacks and to provide a method and a system for dereverberation exhibiting an improved dereverberation of microphone signals.